It is not possible actually to see atom but the nearest possibility to its direct evidence is by using an electron microscope.The image is like  

A clear and accurate image of an object that is smaller then the wavelength of visible light,cannot be obtained.Thus an ordinary optical microscope can measure the size of an object upto or above 500nm(1nm).However,object of the size of an atom can be observed in an electron microscope.

In Pakistan there are only two electron microscopes.

WORKING:

It use beam of electron instead of visible light, because wavelength of electron is much shorter than that of visible light. Electron microscopic photograph of a piece of a graphite which has been magnified about 15 million times.